This invention relates to laser light and more particularly relates to beam splitters for splitting an input laser beam from a single source into multiple output laser beams. The invention more particularly relates to such beam splitters having output beams suitable for being directed to a fiber optic coupler and the use of beams from the fiber optics for therapeutic treatment, such as photodynamic therapy where an undesirable area on a patient, e.g. a tumor, is exposed to a laser beam after absorption by the tumor of a photosensitizing agent such as a porphyrin derivative. More particularly photodynamic therapy is based upon accumulation in tumors of a photosensitizing drug that is activated by visible light to produce a locally cytotoxic agent. For example PHOTOFRIN.RTM., a porphyrin derivative approved for clinical use in the United States, Canada, Europe, and Japan, is activated by 630 nm light. Typically, light emitted from a tunable laser is delivered to a lesion by an optical fiber.
A problem associated with laser medical procedures, e.g. photodynamic therapy, is that often numerous areas on the same patient in fact require treatment. Time involved in setting up and individually treating each of the numerous areas by a single laser source can be extensive often exceeding the useful life of injected photosensitizing compound. Further, sequential treatment results in high cost due to time involved for trained personnel and inefficient use of costly equipment as well as significant discomfort on the part of the patient. It is of course possible to provide multiple laser generators so that multiple areas can be simultaneously treated. Unfortunately, however, the cost for providing multiple laser generators for a single patient treatment is prohibitive.
It is known that laser beams can be split by beam splitters that comprise a partially reflective and partially transparent surface so that an incident laser beam is partially reflected and partially transmitted so that the beam is effectively split into two parts. Unfortunately, there has been no way to practically, consistently or economically commercially manufacture such surfaces so that they all will reflect 50 percent of the beam energy and transmit 50 percent of the beam energy at the same particular incident angle (the angle of the beam to the surface that splits the beam energy in half).
The manufacture of a beam splitter apparatus for more than two output beams thus would have been very difficult since the manufacturing process would have to take the particular incident angle of each individual beam splitter into consideration which requires the calculation of numerous angles of reflection and resulting various alignments and does not permit the use of any kind of standardized set angle hardware within the apparatus. The assembly of such a multiple beam splitter thus would have been tedious, time consuming and unacceptably expensive.
It has thus not been possible to easily and inexpensively manufacture a beam splitter to form four or more output beams where the output beam energies are within ten percent of each other and certainly not within five percent or less of each other.